FIG. 17 is a cross-sectional view of a chain incorporating rolling members , disclosed in Japanese Laid-open Patent Publication No. Sho. 62-4122 (Japanese Examined Patent Publication No. Hei. 4-78523).
The chain 1, shown in FIG. 17, includes a pair of inner link plates 2 spaced from each other in parallel relationship, and connected to a hollow, cylindrical bushing 3. Rolling members 4 are arranged on the outer circumferential surface of the bushing 3, and a roller 5, disposed between the inner link plates 2 surrounds the rolling members 4. Inwardly projecting collars 5a are integrally formed on the ends of the roller 5.
A recess portion 5b, for accommodating the rolling members 4, is formed between the inwardly projecting collars 5a. The collars 5a hold and guide the rolling members 4. A pair of outer link plates 6, spaced and in parallel relationship to each other, is arranged outside the pair of inner link plates 2. The outer link plates 6 are connected to each other by a pin 7, which extends through the hollow, cylindrical bushing 3.
Thrust bearing plates 8 are arranged between the inside surfaces of the inner link plates 2 and the end surfaces of the roller 5. The thrust bearing plates 8 fit onto the outer circumferential surface of the bushing 3 with a clearance. The thrust bearing plates 8 are ring plates made of a material such as a synthetic resin having low friction properties and excellent wear resistance. Suitable materials include fluorine resins, polyamide resins, oil-containing sintered metal, and ceramics.
As shown in FIG. 17, the outer diameter of the roller 5 is larger than the widths of the inner link plates 2 and the outer link plates 6. On the other hand, the outer diameter of the thrust bearing plate 8 is smaller than the widths of the inner link plates 2 and outer link plates 6.
Another conventional chain 11 is shown in cross-sectional view in FIG. 20. In chain 11, a two inner link plates 12, spaced from each other, and in parallel relationship, are connected by a hollow, cylindrical bushing 13. A cylindrical roller 15 is rotatable on the outer circumferential surface of the bushing 13 between the pair of inner link plates 12. Outer link plates 16, also in spaced, parallel relationship to each other, are arranged on the outer sides of the inner link plates 12. The outer link plates 16 are connected to each other by a pin 17, which extends through the bushing 13. The outer diameter of the roller 15 is less than the widths of the inner link plates 12 and outer link plates 16. In chain 11, the roller 15 and the bushing 13 form a slide bearing.
FIG. 21 is a cross-sectional view of a chain 21 incorporating composite rolling members, disclosed in Japanese Laid-open Patent Publication No. Hei. 11-82491. In chain 21, inner link plates 22, which are in spaced, parallel relationship to each other, are connected by a hollow cylindrical bushing 23. Rolling bodies 24 in a holder are arranged on the outer circumferential surface of the bushing 23. A cylindrical roller 25 is disposed between the pair of inner link plates 22 and surrounds the rolling bodies 24 and the holder. Each rolling body 24 comprises a rolling member 24b, and two balls 24c at opposite ends of the roller member, which also serve as rolling members. The holder 24a, as best shown in FIG. 22, is generally cylindrical in shape, and has elongated windows 24d in which the rolling members 24b and balls 24c are accommodated. Outer link plates 26 are arranged in spaced, parallel relationship to each other on the outsides of the pair of inner link plates 22. The outer link plates 26 are connected to each other by a pin 27, which extends through the bushing 23. The outer diameter of the roller 25 is less than the widths of the inner link plates 22 and outer link plates 26.
The chains of the prior art, shown in FIGS. 17-22 are subject to a number of problems. In the case of the chain shown in FIG. 17, for example, since the roller 5 and rolling member 4 are large, the chain 1 itself is heavy and a substantial amount of power is expended just to effect travelling movement of the chain itself.
A second problem with the chain shown in FIG. 17 is that, because the outer diameter of the roller 5 is larger than the widths of the inner link plates 2 and the outer link plates 6, when the roller 5 travels only on a rail R1 as shown in FIG. 1B, the chain is likely to snake. To prevent snaking of the chain 1 it is necessary to provide a rail R2 with a recess for guiding the roller 5, as shown in FIG. 19. However, the time and effort required to provide the rail R2 with a recess leads to substantial increase in the cost of the equipment which utilizes the chain.
A third problem is that the formation of the integral inwardly extending collar 5a on the roller 5 requires the cutting or grinding of a recess portion 5b in the interior of the roller. The cutting or grinding process is time-consuming and difficult, resulting in low productivity and increased cost.
A fourth problem is that, since the outer diameter of the roller 5 is large, shock and wear are likely to occur as the chain meshes with a sprocket.
A fifth problem is that attachments and conveyed materials can interfere with a portion of the roller 5 projecting beyond the inner link plates 2 and the outer link plates 6.
A sixth problem is that, although the rolling members 4 are arranged between the bushing 3 and the roller 5, an axial thrust load applied to the roller 5, results in skew of the rolling members 4 (that is, tilting of the rolling members 4 with respective to their proper axes of rotation). Thus, wearing and locking of the rolling members 4 can occur, preventing the rolling members 4 from rotating. This, in turn, prevents the roller 5 from rotating smoothly.
The chain 11 shown in FIG. 20 has no rolling members between its roller 15 and its bushing 13. The need for frequent oiling due to the sliding contact between the roller 15 and the bushing 13, requires many man-hours for maintenance.
A second problem with the chain of FIG. 20 is that heat generated due to the sliding contact between the roller 15 and the bushing 13 can exercise an adverse effect on material carried by the chain.
A third problem is that there is a relatively high coefficient of friction between the roller 15 and the bushing 13 because of their sliding contact, and consequently more power is required to move the chain.
A fourth problem is that, when a thrust load is applied to the chain 11, an end surface of the roller 15 slides against an inside surface of one of the inner link plates 12, generating wear, which reduces the thickness of the link plate 12 and reduces its breaking strength. Consequently, the inner link plates 12, the strength of which is essential to the tensile strength and integrity of the chain, are subject to breakage.
The chain 21 shown in FIG. 21 is also subject to several problems. First, when a thrust load is applied to the chain 21, an end surface of the roller 25 slides against an inside surface of one of the inner link plates 22, generating a large amount of wear. As in the case of the chain of FIG. 20, the thickness and strength of the inner link plates 22, which are essential to the tensile strength of the chain, decrease due to wear. Consequently the breaking strength of the inner link plates 22 is decreased and their breakage can result in failure of the chain.
Secondly, when a thrust load is applied to the chain, a ball 24c, which is on an end of a rolling member 24b, is loaded heavily, and the increased stress applied to the ball 24c causes rapid wear.
A third problem with the chain of FIG. 21 is that, because each rolling body 24 comprises not only a rolling member 24b, but also two balls 24c arranged at opposite ends of the roller member, 24b rolling member 24b, the component count in the chain is high, which results in high manufacturing cost and difficult assembly.